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Much Less Dark Matter in Early Galaxies

03/20/2017 7:48 AM

I came across this interesting article on the Scientific American website and thought I would pass it along.

Dark Matter Did Not Dominate Early Galaxies

Although the invisible substance known as dark matter dominates galaxies nowadays, it was apparently only a minor ingredient of galaxies in the early universe, a new study finds. This new finding sheds light on how galaxies and their mysterious "haloes" of dark matter have changed over time, researchers said.

Dark matter is thought to make up about 84 percent of the matter in the universe. Although dark matter is invisible, its presence can be inferred by its gravitational effects on visible matter. For instance, previous work discovered that the outer parts of galactic disks whirl faster than expected around the cores of those galaxies. These findings make sense if one assumes that "haloes" of dark matter envelop those galaxies and gravitationally pull at their outer regions. Now, the researchers unexpectedly find that in the early universe, dark matter played a much smaller role in galaxies than previously thought. The scientists detailed their findings in the March 16 issue of the journal Nature. Using the European Southern Observatory's Very Large Telescope in Chile, the researchers examined six massive, star-forming galaxies from the early universe during the peak of galaxy formation 10 billion years ago. They analyzed the rotation of these galaxies to calculate how much dark matter they possessed.

When it comes to the Milky Way and other typical galaxies born in the current era of the universe, their "effective radius"—that is, the bright region that half their light comes from—is 50 to 80 percent dark matter, said study lead author Reinhard Genzel, an astrophysicist and director of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany. In comparison, in half the early galaxies the researchers studied, dark matter made up 10 percent or less of the galaxies' effective radius, Genzel said. The researchers also looked at about 100 other, fainter galaxies. They discovered that, on average, data from these galaxies agreed with their findings.

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#1

Re: Much Less Dark Matter in Early Galaxies

03/20/2017 9:22 AM

Interesting. I'm probably reading too much into this but this does support one of my pet theories on this phenomena. If more "new" space between interstellar objects is being generated now than in the past then this might account for at least part of the missing force known as dark matter.

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#6
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Re: Much Less Dark Matter in Early Galaxies

03/20/2017 1:51 PM

Bottom line: We are doomed. We have to warp into another dimension, only to be crushed by hyper-present gravity force equivalent to nuclear strong force in that dimension. We are still doomed.

If the Universe started out with light only, and the balance is seeking to rest with all mass, then accumulation in the supermassive black holes at the center of galaxies seems consistent, but how does energy keep being converted to mass over time far from the discontinuity in space-time continuum at the origin point?

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#7
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Re: Much Less Dark Matter in Early Galaxies

03/20/2017 2:09 PM

Of course we are all doomed. Everyone dies.

I'm disturbed that you chose my comment to reply with such a non-sequitur comment. How does anything you've said here have anything to do with either dark matter or this discovery that there was less dark matter in the extreme past?

Do I upset you so much that you have to stalk my comments?

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#8
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Re: Much Less Dark Matter in Early Galaxies

03/20/2017 2:31 PM

Did not mean to, oops! Heck, I could not see any velocity difference between the "new" galaxy, and the "old" one, so were they referring to Doppler shifts differences between near and far?

Sorry about the non-sequitur, I meant it to be that this dark matter (that does not interact with E-M radiation), but does act gravitationally in a similar way to matter, seems to be getting more massive....right?

Where does it get more mass, since there is no A&P around the corner?

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#9
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Re: Much Less Dark Matter in Early Galaxies

03/20/2017 3:12 PM

The curved arrows in the left-hand picture demonstrate what astronomers see when looking at distant galaxies; the image in the right-hand picture is what astronomers would expect to see based on Newtonian (or even Einsteinian) gravity and the estimated amount of matter in the galaxies.

That is to say in general, the spiral arms of any given galaxy are moving much faster around the galactic nucleus than makes sense based on visual and radio observations of the amount of matter there and how the matter is distributed. It's as if the galaxies move almost like a solid wheel rather than a collection of individual stars and gas clouds in 'free fall' orbits due to gravity.

Various theories have been proposed to explain this discrepancy between basic physics and the observations. There are (as far as I know) two main theories: Dark Matter we don't/can't see, and a modification to Newtonian/Einsteinian gravity known as MOND (Modified Newtonian Dynamics) which proposes a modification of Newtonian gravity. The lead theorist on this is Mordehai Milgrom

From Wikipedia: "Since Milgrom's original proposal, MOND has successfully predicted a variety of galactic phenomena that are difficult to understand from a dark matter perspective. However, MOND and its generalisations do not adequately account for observed properties of galaxy clusters, and no satisfactory cosmological model has been constructed from the theory."

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#10
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Re: Much Less Dark Matter in Early Galaxies

03/20/2017 3:23 PM

I heard something on one of the Science Channel programs that indicated some of this velocity is due to magnetic field effects (that are apparently pretty strong, and they can apparently measure line splitting of atomic and ionic spectra of cooler gases between stars to show the Zeeman splitting of those lines.

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#13
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Re: Much Less Dark Matter in Early Galaxies

03/20/2017 6:07 PM

They do seem to be portraying it as a discrepancy between observation and expectations/theory, but that might be making the problem more difficult to discover.

The `observation' in this case is not reasonably free of 'expectation/theory'. How are the speeds of rotation being determined. This isn't as simple as mile marker and stop watch. If something about speed is being inferred from indications of probable mass, just to note there is a discrepancy with distribution of that mass, there is a problem closer to home. If the velocity is determined by redshirt of assumed known frequency sources, that is not without significant reliance on theory and assumption as well.

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#15
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Re: Much Less Dark Matter in Early Galaxies

03/21/2017 9:56 AM

The speeds of rotation are determined by looking at the doppler shift of light from the two sides of a galaxy. As you know, the doppler shift of something moving away shifts a spectral line toward longer wavelengths ('red shift') and conversely something approaching is 'blue shifted'. These observations are done both at optical wavelengths and at radio wavelengths. For radio studies, they typically look at the 21cm spectral line of hydrogen. So as the galaxy spins, the spiral arms on one side are moving toward the Earth and the ones on the other side are moving away from the Earth, compared to the galaxy's central nucleus. And by studying the doppler shift they can plot a graph of velocity vs distance from the central nucleus.

Measuring the doppler shift isn't all that difficult. I've taken a low-resolution spectrum of Saturn which is spinning much, much slower than any galaxy. A trained eye can pick out a slight shift in the spectrum in the two sides of Saturn's rings even at their slow speed.

Wikipedia provides a pretty good article about the whole subject, including mentions of dark matter and MOND. https://en.wikipedia.org/wiki/Galaxy_rotation_curve

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#16
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Re: Much Less Dark Matter in Early Galaxies

03/21/2017 10:04 AM

Nice picture and a great demonstration of how visible light Doppler shift measurements can be performed.

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#17
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Re: Much Less Dark Matter in Early Galaxies

03/21/2017 3:34 PM

Okay, let's assume that there are zero effects on wavelegths from things like relativistic effect on fusion within stars moving at very fast speeds toward of away from us....and that all the other math adds up with nothing significant overlooked....

.

Doesn't it still feel like we are making the same mistake, twice?

.

Einstein made what he considered to be his biggest blunder because he assumed the size of the Universe was relatively static and inserted a 'cosmological constant' to fit to that model instead of an expanding Universe.

We seem to be headed with full certainty down the same path, assuming that galaxies must be relatively static in size, i.e. that the speeds of rotation must correspond to stable orbits and not rapidly expanding galaxies. We are so certain that we have conjured invisible matter in the sky...in special shapes.

If the universe is expanding, maybe it isn't such a far out idea that things on a slightly smaller scale are doing the same. Maybe gravity was stronger in the past? Maybe inertial effects of mass were weaker in the past? Maybe we can actually see all the matter.

It's going to be a while before we can see if the galaxies are actually making the curve we assume, right?

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#19
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Re: Much Less Dark Matter in Early Galaxies

03/21/2017 8:06 PM

Astronomers are looking at galaxies across a huge range of space - in all different directions and at distances from relatively nearby like the Andromeda Galaxy, to spiral galaxies near our cosmic horizon. That spans a range of time covering around 10 billion years. Yet, 'young' and 'old' spiral galaxies look pretty much the same. In general the only evolution seen is the ages of the stars in the galaxies.

If there was some kind of expansion going on, or other evolutionary process due to some cosmic force like gravity or electromagnetism or something else, it would likely have been seen by now. The Hubble telescope should have found it.

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#20
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Re: Much Less Dark Matter in Early Galaxies

03/21/2017 9:49 PM

".....Yet, 'young' and 'old' spiral galaxies look pretty much the same..."

.

Are you sure about that? That would be a pretty strange result if galaxies formed and existing through conditions that changed significantly looked pretty much the same as the earliest galaxies we can see by looking the furthest.

Seems like galaxies would evolve, just like stars, just like solar systems, to look different when older than when young. Looking far enough back should limit the available time for galaxies to mature. If some of the closer galaxies don't appear more mature, it would suggest fjndamental problems in some of the basic ideas, right?

This article in particular points out what seem to be very significant differences between what we see of galaxies long ago and more recent light from galaxies that have had all the time to mature.

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#25
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Re: Much Less Dark Matter in Early Galaxies

03/22/2017 9:32 AM

Didn't we read somewhere a few weeks ago of a new controversial discovery that found red shifts seemed to be correlated more with galactic shape (type of galaxy) than with the supposed distance (derived independently from Doppler measurement by standard candle, angular aperture, etc.)?

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#21
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Re: Much Less Dark Matter in Early Galaxies

03/22/2017 1:08 AM

So are you saying that the upper left portion of the ring is more blue and the lower right portion of the ring more red?

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#22
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Re: Much Less Dark Matter in Early Galaxies

03/22/2017 1:41 AM

Okay, sorry to keep pestering you about this....

What variation in wavelength would you suppose the human eye can reliably detect? Do you think you can discern reliably between 500 nm and 501 nm? 500.0 nm and 500.1 nm?

If the advancing and receding rings total to less than 50 km /s, the change would be smaller than that, I think.

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#23
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Re: Much Less Dark Matter in Early Galaxies

03/22/2017 7:31 AM

No, not more blue or red (well, very slightly), since this is a broad spectrum. If the spectrum was high resolution one might see a small shift in any spectral lines from the sunlight reflected off the rings.

Astronomers use photodetectors to scan the spectra, not their own eyes. The detectors are attached to spectrometers. The combination can be far more precise than human eyes, though of course once the data is gathered the astronomer can plot and examine the spectrum in fine detail.

Here's an article about a galaxy that is suspected of being mostly dark matter. (Though actually, I lean toward the MOND theory.)

http://www.keckobservatory.org/recent/entry/scientists_discover_massive_galaxy_made_of_99.99_percent_dark_matter

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#24
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Re: Much Less Dark Matter in Early Galaxies

03/22/2017 7:58 AM

So help me out here. What are you seeing in the photograph of Saturn's rings if not a shift toward red and shift toward blue on the opposite side?

Which is receding and which side is advancing in the picture?

Shouldn't we be seeing the greatest shift or other effect on the rings closest, as these will be orbiting fastest?

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#12
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Re: Much Less Dark Matter in Early Galaxies

03/20/2017 3:56 PM

some chicks said when you go black/dark you can't go back. I don't know if its true.

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#11
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Re: Much Less Dark Matter in Early Galaxies

03/20/2017 3:27 PM

So you are saying the new "space" is resulting in apparently higher velocities now?

I don't get how things automatically accelerate because of the "new space". Doesn't that still require some sort of force?

Hey, I am just trying to get a few of my neurons (that aren't lying down kicking sideways) to wrap around some of these concepts, and it is getting harder the older I get.

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#14
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Re: Much Less Dark Matter in Early Galaxies

03/20/2017 10:51 PM

The "new space" appeared between the stars of the less distant galaxy without those stars moving through space. My pet theory is that baryon mass concentrations (stars, planets, globular clusters, etc.) locally stabilize space to prevent "new space" from forming. Gravity attenuates by the inverse square law only in stabilized space. I believe this agrees with the inflationary period for baryons were not coalesced until after inflation happened. This also agrees with the dark energy paradox. As we look out through more empty space there is more expanding space between luminous objects.

I'm certain my layman's theory has plenty of inaccurate issues. Then again AFAIK all "approved" theories have issues, too.

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#2

Re: Much Less Dark Matter in Early Galaxies

03/20/2017 9:22 AM

I'd believe if they caught one.

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#3

Re: Much Less Dark Matter in Early Galaxies

03/20/2017 9:45 AM

Maybe, since it interacts with normal matter through gravity, it shouldn't be a surprise that over time it has accumulated in the centers of galaxies.

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#4

Re: Much Less Dark Matter in Early Galaxies

03/20/2017 10:34 AM

Isn't this the exhaust from black holes?

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#5

Re: Much Less Dark Matter in Early Galaxies

03/20/2017 12:13 PM

Could it simply be that (dark matter) is just the accumulated (smog) that results from (young) stars just starting out to (hot rod) around around the universe?...

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#18

Re: Much Less Dark Matter in Early Galaxies

03/21/2017 3:35 PM

This supports my conjecture that dark matter is just black holes and the space between them.

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